Conventionally, there have existed refrigerating apparatuses each having, for example, a refrigeration cycle unit provided at a high temperature side (upper stage side, primary side) (hereinafter referred to as a high temperature side cycle), and a refrigeration cycle unit provided at a low temperature side (lower stage side, secondary side) (hereinafter referred to as a low temperature side cycle), the refrigeration cycles being configured in a multi-stage manner (here, a cascade refrigerating apparatus having a two-stage structure is referred to). In such refrigerating apparatuses as described above, by exchanging heat with an object to be cooled, or the like in an evaporator of the low temperature side cycle which becomes a final stage while, for example, exchanging heat between condensation heat generated by condensation of a refrigerant in the low temperature side cycle and evaporation heat generated by evaporation of a refrigerant in the high temperature side cycle, a coordinated refrigerating operation is performed. As a result, in the evaporator of the low temperature side cycle, evaporation heat at a low temperature, that is, at several tens of degree of temperature below the freezing point can be obtained with high efficiency.
Some of such cascade refrigerating apparatuses as described above exist in which a hydrocarbon-based refrigerant having a low global warming potential (GWP) is used as a refrigerant to circulate in the high temperature side cycle, and carbon dioxide is used as a refrigerant to circulate in the low temperature side cycle from the standpoint of preventing global warming (for example, refer to patent literature 1).